How did Cathcart get Jardine to go to Galt's apartment?

When Hardy tells Mari that "a man who chases a rich man's wife" can be tempted with money, I inferred he told Tony that he'd hired Brad to pay Tony off to drop his wife and skip town.

What I don't get is why someone like Cathcart would harass Galt in the first place. He had nothing to do with their altercation in S.F. Had he already suspected that Mari and Tony were diddling, and he'd set up Brad as a fall guy due to the prior problem between Tony and Brad? I guess Brad demonstrated he could be set up, as Jardine was no Brainiac and had Brad sent away for two years.